The objective of this project is the production of standardizec, well-characterized reference antisera to the immune response-associated (ia) antigens of the laboratory mouse. During each of three years a total of 2,000 ml. on antiserum will be produced, divided among 4 or 5 different ia specificities per year. Each antiserum will be analyzed to determine its titer and specificity, then divided into aliquots for distribution.